A cutting tool for rotary chip removing machining of workpieces includes a basic body and a number of cutting inserts, as well as in some cases shim plates mounted between the cutting insert and the basic body as a protection for the basic body. The basic body is formed so that it has a center axis, i.e., a rotational axis, as well as a peripheral envelope surface, a front and a rear end surface, and a number of chip pockets, in which insert seats are arranged. Each insert seat is adapted for the mounting of a cutting insert and a shim plate. The chip pockets are adapted so that the chip release in the machining should work without problems.
Shim plates are used in cutting tools to decrease the wear of the basic body and thereby increase the service life of the basic body. In addition, the shim plate decreases the risk of serious damage to the basic body upon a possible insert breakdown. Insert breakdowns almost exclusively occur at the main edge of the cutting insert, i.e., the active cutting edge at the envelope surface of the basic body. The shim plate, placed between the cutting insert and the basic body, can then continue to remove chips from the workpiece in the period of time it takes to interrupt the progressing machining. Without a shim plate, there is risk of the basic body getting stuck in the workpiece leading to damage to the basic body, the spindle that drives the cutting tool, as well as to other co-operating parts in the machine tool in which the cutting tool is included. Therefore, it is desirable to use a shim plate. The shim plate is mounted between the basic body and the cutting insert in such a way that the bottom surface of the cutting insert rests against the shim plate, while the possible other support surfaces of the cutting insert abut against the basic body of the cutting tool. The ways to fix the shim plate in the basic body vary; for example, they can be attached together with the cutting insert by a simple screw, or a tubular screw having a threaded inside can be used to attach the shim plate, so that the cutting insert easily can be attached to the tubular screw and be replaced without the shim plate needing to be removed. Shim plates of the usual plane type intended for milling tools are, for example, disclosed in WO2006130073. The shim plate disclosed therein includes a coupling to prevent sliding in relation to the basic body.
A disadvantage of shim plates is that they decrease the strength of the basic body, since the insert seat has to be made deeper to make room for the shim plate for the size of the chip pockets not to be affected. Since the size of the chip pockets is optimized in respect of chip release, it is not desirable to decrease the same. The force that acts on the cutting tool in the machining varies, among other things depending on the cutting depth and on the type of machining and material. In milling, the force is however primarily directed so that a deepening of the insert seat to make room for a shim plate significantly affects the strength. For small cutting tools, such as shank-end mills, and for tools having many cutting inserts mounted, this becomes particularly problematic since the chip pockets proportionally already occupy a great part of the basic body. The strength of the basic body is considerably impaired by a further deepening of the insert seats and the risk will be too great that cracks, as a consequence of overloading, should arise in the basic body upon machining.
The present invention aims at increasing the service life of cutting tools for rotary chip removing machining, henceforth called cutting tools, at the same time as the strength of the basic body of the cutting tool is maintained. This applies particularly to small cutting tools, for example shank-end mills, or to cutting tools having many cutting inserts.